1. Field of the Invention
The present invention relates to novel crystalline alumina compositions and methods of making the compositions, to articles made from the compositions, and to catalyst systems and methods utilizing the compositions. In another aspect, the present invention relates to novel thermally and hydro-thermally stable, substantially phase-pure, crystalline alumina compositions that are similar, if not identical to, .delta.-alumina compositions, to methods of making the compositions from boehmite or pseudo boehmite, and to catalyst supports made from such compositions.
2. Description of the Related Art
Gaseous waste products resulting from the combustion or incomplete combustion of hydrocarbonaceous fuels, such as gasoline and fuel oils, generally include carbon monoxide, hydrocarbons and/or nitrogen oxides. These waste products pose a serious health problem with respect to pollution of the atmosphere. Sources of such gases include exhaust from stationary engines, industrial furnaces, and vehicle engines.
The amount of waste products in such exhaust gases must generally be removed to levels established by government environmental regulations. Typically, this is done by placing in the exhaust stream catalysts which are capable of removing carbon monoxide, hydrocarbons and nitrogen oxides at the same time.
Such catalysts for treating such exhaust gases are well known in the art. More specifically, these catalysts contain platinum, palladium and/or rhodium and are known as three-way catalysts, and may also include other stabilizers and promoters to improve the activity of these catalysts. However, these catalysts have characteristically tended to lose surface area or become otherwise unstable over time and extended use, particularly at high temperatures, i.e., those above about 1000.degree. C.
For the past twenty years or so, tightening environmental regulations have provided the incentive to improve the performance of such engine exhaust catalysts. The art is replete with numerous patents and articles directed toward such catalysts. However, in spite of the number of prior art catalyst systems, there is a never-ending search for improving catalyst technology, particularly for catalyst systems that are thermally and hydrothermally stable.
For example, there is a need in the art for a .delta.-alumina composition that is stable against loss of surface area and phase integrity when exposed to repeated and/or extended use at temperatures in excess of 1000.degree. C.
There is also a need in the art for engine exhaust catalyst supports made from a thermally stable .delta.-alumina composition. Another need in the art is for a catalyst system having at least one catalytically active component on a thermally stable .delta.-alumina composition. Still another need in the art is for a method of purifying automotive and other engine exhausts utilizing a catalyst system having an active component on a thermally stable .delta.-alumina composition.
That these and other needs in the art have been met by this invention will become apparent to those of skill in the art upon review of this specification.